Encoders are classified as “sensors”. Rotary encoders sense rotary motion. A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to an analog, digital or other code. Because encoders sense rotary motion and provide signals that can be used to measure and control that motion, they are used in closed-loop motion control systems in which the encoder acts as the feedback device.
The output of the incremental encoder provides information about the motion of the shaft that is further processed elsewhere into information such as speed, distance, revolutions per minute (RPM), acceleration/deceleration and position. Rotary encoders are used in many applications that require precise shaft unlimited rotation, including industrial controls, robotics, elevators, escalators, moving walkways, medical applications, military applications, automotive applications, servo/brush/brushless and stepper motor feedback and many other applications.
An incremental rotary encoder provides cyclical outputs when the encoder's shaft is rotated. The incremental rotary encoder is the most widely used of all rotary encoders due to its low cost and the ability to provide signals that are easily used to provide motion related information such as velocity and RPM.
Rotary encoders are used to track the position of the motor shaft on permanent magnet brushless motors, which are commonly used on computer numerical control (CNC) machines, robots and other industrial equipment. Incremental (quadrature) encoders are used on induction motor type servomotors. In these applications a feedback device (encoder) plays a vital role in ensuring the equipment operates properly. The encoder synchronizes a relative rotor magnet and stator winding positions to the current provided by the drive. Maximum torque results if the current is applied to the winding when the rotor magnets are in a particular position range relative to the stator windings. The motor performs poorly or not at all if timing is not adjusted correctly. Improper encoder alignment on the motor actually causes it to run backwards resulting in a hazardous run away condition. Correct alignment is essential to proper operation of these motors.
Traditional optical encoders utilize ball bearings, flexible couplings, bushings, and shafts, and incorporate manual or machine optical alignment during manufacture and other expensive components or manufacturing steps to produce a reliable and accurate rotary optical encoder.
The majority of rotary encoders produced today utilize a set of ball bearings to create a stable platform on which the encoder operates. This is made necessary due to the fact that the air gap and alignment between the rotating disc in the encoder and the adjacent sensor must be accurately controlled especially in high line count encoders. In addition, the ball bearings are forced to transmit all motor shaft motion irregularities to all of the encoder components.
It is therefore an object of the present invention to substitute a new and innovative method of bringing the active elements of the encoder into alignment and holding that alignment at a minimum of cost. It is a further object of the present invention to provide parts that are injection molded from advanced plastic compounds to further reduce cost, assembly labor, and improve overall performance and reliability. Encoders are well suited for systems that measure rate-of-movement variables such as velocity and RPM. In certain applications they may be used to measure distance of linear motion (e.g. feet or inches of movement).
Encoders themselves do not do the counting or the control function. Rather, the counting is done in the external electronics. Although it would be possible to introduce the external control functions within the encoder; this possibility is considered within the scope of this patent. The point at which the counting begins is controlled by electronics located externally and/or internally on the circuit board. The circuit board is not material to the interpretation of this patent.
There are various methods used by encoders to reference shaft position. Transmissive optical type encoders utilize an LED(s), a transparent disc, and sensor(s). Perforated optical type encoders utilize an LED(s), a solid disc with perforations, and sensor(s). Magnetic type encoders utilize magnetic components and a sensor(s). Reflective type encoders utilize a reflective surface, LED(s), and sensor(s). Within these types of encoders, there are categories that divide the various styles further. There are also absolute rotary encoders (single turn and multiple turn) that give position without the need to count to track shaft location, but rather give a direct reading of location from various codes recorded on the disc. Upon power up, an incremental encoder must go to a “home” position to begin a controlled move whereas an absolute encoder will know it's location upon powering up the encoder's electronics. There may be other encoding techniques yet to be developed and this patent will apply equally to those as well. Most of the details of this document will be described by the reflective style encoder, but can be interpreted to include the other styles described.
The present invention describes the design of a component that modifies the design of the previous mentioned encoder styles. It is a component that can be integrated into the various previously mentioned encoder styles or new encoder styles in numerous ways.